Revealing the mechanism of saturated ether electrolyte for improving the long-cycling stability of Na-O2 batteries

Abstract

Na-O2 batteries have been considered as promising energy storage systems due to their high energy density and low cost. Their poor cycle life, however, and their unclear interfacial formation mechanisms have greatly hindered the development of Na-O2 batteries. In this work, compared to the commonly used ether-based electrolyte (0.5 M sodium trifluomethanesulfonate in tetraethylene glycol dimethyl ether), its saturated electrolyte is employed for Na-O2 batteries to achieve around four times longer cycle life. Both experiments and simulations suggest that the enhanced cycling stability could be attributed to the use of saturated electrolyte, which plays important roles in reducing the dissolution of NaO2, thereby easing the shuttle effect of O2-; sharply decreasing dissolved oxygen, thus eliminating Na anode oxidation; and effectively suppressing Na dendrite growth because of the high Na+ flux in saturated electrolyte, thus relieving the nonuniformity of the Na+ flux.